This invention relates to a polyether having silicon end group, and a composition comprising said polyether, which is changeable to a rubber-like substance upon exposure to atmospheric moisture at room temperature and which is useable as a sealing materail or adhesive.
In the prior art, there are both two component type and single component type of sealing or adhesive material which can vulcanize at room temperature.
Some examples of the two component type of sealing or adhesive material are chemical compounds of the thiokol series, urethane series, etc. In such two component systems, it is necessary to mix a main component and a vulcanizer prior to use. This leads to many disadvantages, such as the same adhesive properties are not always reproducible since method of mixing, and mixing conditions are rarely reproducible. Thus, the entire amount of the mixed material must be used promptly. In order to overcome these disadvantages, sealing materials of the single component type have been developed.
One example of sealing materials of the single component type is a polymeric substance having isocyanate end group. However, although some of the problems arising from use of two component type of sealing material are resolved, there are still many unsolved problems with the single component type. For example, although the polymer having isocyanate end group has an advantage in that it vulcanizes upon contact with the atmospheric moisture at room temperature, it has many disadvantages, such as it bubbles upon vulcanization due to carbon dioxide being generated and consequently, poor adhesive properties of the resulting polymer are produced. Moreover, it cannot be used as a sealing material at temperatures higher than 80.degree.C since the thermal stability of the resulting polymer is poor. Also, its vulcanizing velocity is relatively slow.
Another example of a single component sealing material is polysiloxane having silicon end group provided with one or more hydrosyzable groups. The polymer is able to vulcanize rapidly by contact with atmospheric moisture without producing any undesirable phenomenon, such as bubbling caused by generation of gaseous reaction products. Moreover, the adhesive property and the thermal stability of the resulting polymer are excellent. However, since the polymer consists of a special kind of main chain as polysiloxane in its molecular structure, a large commercial disadvantage arises from its high cost. Accordingly, work has been done to obtainpolymers whose main chains do not consist of polysiloxane and instead consists of organic polymer of low cost and having silicon end group only at each end of the molecular chain and wherein silicon atom has at least one hydrolizable group.
In order to obtain such organic polymers having silicon end group provided with hydrolyzable groups, the following two methods have been proposed for synthesizing same; namely, Method "A" as set forth in U.S. Pat. No. 3,592,795 and 3,408,321 and Method "B" as set forth in U.S. Pat. No. 3,632,557.
A method B, a polymer having hydroxyl end group such as polyether polyol or polyester polyol is used as a starting material for synthesis. First, a polymer having two isocyanate end groups connecting to each chain end with at least two urethane linkages in a molecule, is synthesized by the reaction of the polymer having hydroxyl end group with isocyanate compound such as toluene, diisocyanate. Then, an organic polymer having silicon end group provided with hydrolyzable groups is finally synthesized by the reaction of isocyanate group of the obtained polymer of the first step with a special organo-silicon compound such as .gamma.-aminoproply trimethoxy silane. This final product is useful as a sealing material of the single component type. The product has functional groups at both ends of each molecule, which are very sensitive to the atmospheric moisture and easily changed by hydrolysis to hydroxyl groups which are capable of rapid condensation reaction between them to produce vulcanized polymer.
However, in Method B, disadvantagesouly, since such expensive starting materials as isocyanate and .gamma.-aminopropyl trimethoxy silane are used for synthesis, the production cost of the polymer having silicon end group becomes unexpectedly high. It is generally necessary to have a molecular weight of the main chain in an organic polymer of more than 10,000 to obtain a sufficient elongation of the resulting polymer vulcanized by polycondensation between the hydroxyl groups attached to the silicon end groups in the organic polymer having silicon end groups. In order to increase the molecular weight of the polymer having hydroxyl end group to that sufficient weight, as a starting material for the synthesis, it is convenient to combine the polymer molecules through urethane linkages by reaction with an isocyanate compound. Generally, since the molecular weight of a polymer having hydroxyl end group is about 2,000 at the highest, the polymer having an enhanced molecular weight of more than 10,000 obtained by the reaction with an isocyanate compound should have many urethane linkages in each molecule. As is well known, since the urethane linkage has a strong tendency to make a hydrogen bond intermolecularly, the viscosity of the obtained polymer in Method B, is so high that handling of the polymer becomes difficult and inconvenient. Furthermore, since the viscosity of the polymer is so high, it becomes impossible to mix in a large amount of fillers which are cheaper material and which reduce the cost of sealing materials. Also, since there exist many urethane linkages in the polymer, other problems involving thermal stability and mechanical property arise. For example, a sealed article with a sealing material obtained by Method B become impossible to use afterwards when heated in an oven at or above 120.degree.C. Furthermore, although the mechanical strength of the vulcanized polymer is sufficiently large for practical use, its elongation is too small. This latter property produces a great disadvantage to the polymer obtained by the method B when used as a sealing agent. If a vulcanized sealing material has only a small breaking elongation, even though it has a large mechanical strength, it has a tendency to separate rather easily from a surface of adhered article or sometimes the adhered article itself will break.
In Method A, a polymer having hydroxyl end group, such as polyether polyol or polyester polyol is used as starting material for synthesis. First, a polymer having olefine end group is bonded to main chain through urethane linkage, and in the next step an organic polymer having silicon end group is synthesized by the reaction of the polymer having olefine end group with a silicon hydride compound in the presence of a platinum catalyst.
One typical example of the methods used for preparing polymers having an olefine end group bonded through urethane linkage, involves reacting a polymer having hydroxyl end group with allyl isocyanate. In the method, first, an isocyanate compound, such as toluene diisocyanate is reacted to a polymer having hydroxyl end group to derive a polymer having isocyanate end group. Then, finally, a compound such as allyl alcohol is reacted to the isocyanate end group. Therefore, the polymer having an olefine end group prepared by the method of A has at least two urethane linkages per one molecule and moreover has active hydrogens originated from nitrogen-hydrogen bonds in the molecule. In Method A, the organic polymer having silicon end group is further synthesized by hydrosilylation of the polymer with a silicon hydride.
There is a problem to this reaction. The silicon hydride adds to the olefine linkage and reacts with active hydrogen existing in the urethane linkage and is consumed. Especially, when a halo-silane compound, which is relatively inexpensive and has high reactivity, such as dimethyl chlorosilane or trichlorosilane, is used, very rapid reaction between the halosilane compound and the urethane linkage in the polymer occurs. Accordingly, the desired reaction of hydrosilylation is almost hindered. Therefore, practically, the halogenated silicon hydride cannot be used in this synthesis. A silicon hydride not containing halogen atoms, such as methyl dimethoxy silane or methyl diacetoxyl silane, etc, should instead, be used. The cost for production of a polymer having such silicon end group is high, since the price of the silicon hydride is high. Moreover, disadvantageously, it is necessary to use a large amount of special platinum catalyst of high cost for hydrosilylation in order to increase the reaction velocity for addition of the silicon hydride to olefine end group.
Furthermore, although polyoxypropylene glycol is mainly used as a starting material in Method A, from the standpoint of production of polyoxypropylene glycol itself, the molecular weight of polyoxypropylene glycol should be restricted to within 3,000 at the highest, in order to obtain a polymer having two hydroxyl groups at both ends of each molecule. Accordingly, it is necessary to use such a polyoxypropylene glycol of low molecular weight of 3,000 at the highest, as a starting material of Method A.
This produces a polymer of low molecular weight, having silicon end group, in Method A. As already mentioned, the breaking elongation of the cured polymer resulting from such a polymer of low molecular weight (lower than 3,000) is very small. Accordingly, and practically, the polymer produced by Method A can be hardly used as a sealing material.
As discussed above, the organic polymers having silicon end groups which have been proposed to data, have many disadvantages and as yet unsolved problems.